This invention concerns the purification of crude aqueous alkanesulfonic acid containing oxidizable impurities. More particularly, it relates to the use of chlorine treatment of such crude material to convert the oxidizable impurities to alkanesulfonyl chloride and thereafter hydrolyzing the alkanesulfonyl chloride to alkanesulfonic acid.
In the manufacture of alkanesulfonic acid by the reaction of an alkyl mercaptan or dialkyl disulfide with chlorine and aqueous hydrochloric acid at elevated temperature, a crude aqueous (20-35 wt. % water) alkanesulfonic acid containing oxidizable impurities is first formed. Dialkyl disulfide, alkyl alkane thiosulfonate and alkanesulfonyl chloride are the principal stable intermediates in this process. The total of dialkyl disulfide and alkyl alkane thiosulfonate is referred to as oxidizable impurities in the crude aqueous product. The crude product may be purified by heat stripping. Heat stripping, usually steam stripping, removes some of the oxidizable impurities overhead from the crude product but unexceptable levels remain and the bottoms product of the stripper must be further treated, e.g., by reaction with hydrogen peroxide or ozone, to reduce or eliminate the impurities.